The Australian government is refusing to back an independent international investigation into alleged war crimes during the Sri Lankan civil war as the government of the island nation rejected a new report detailing "credible" claims of civilian bombings, extrajudicial killings and other abuses.

The United Nations Human Rights Council is due to consider a new resolution on the allegations next month. Britain and Canada have already called for an international inquiry, saying Sri Lanka has failed to heed two previous UN resolutions for it to launch its own judicial inquiry and prosecutions.

There are reports the US will sponsor the resolution for an international inquiry.

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Asked if Australia supported a UN-sponsored investigation and would co-sponsor any resolution, Minister for Foreign Affairs Julie Bishop was non-committal.

"The Australian government has consistently urged Sri Lanka to ensure that all allegations of serious international crimes committed by both sides to the conflict are investigated and prosecuted in a transparent and independent manner," she said in a statement.

"Any future formal investigation would need to be agreed by the international community and would be a matter for relevant bodies at the time."

Sri Lanka's high commissioner to Australia, Admiral Thisara Samarasinghe, rejected the allegations in the report by the Public Interest Advocacy Centre released on Wednesday. The report outlined evidence that Sri Lankan security forces corralled civilians into no-fire zones and then launched artillery on them, and had assassinated rebel soldiers as they tried to surrender.

"These are unsubstantiated and biased speculations orchestrated by a defeated terrorist organisation," he said, referring to the Liberation Tigers of Tamil Eelam or Tamil Tigers.

The PIAC Report, which interviewed 30 witnesses and examined other material, found there was considerable evidence that suggests both sides in the conflict had committed war crimes or crimes against humanity but the victorious Sri Lankan government was responsible for the "vast majority" of them.

It said there was enough evidence to bring senior military and government officials in Sri Lanka to trial before an international court.

Admiral Samarasinghe said the report was designed to whip up sentiment ahead of the UN meeting and that there needed to be more respect for the strides Sri Lanka had made in reconciling the country after almost 30 years of conflict.

Australia is not a member of the UN Human Rights Council but co-sponsored the two previous resolutions calling for action by Sri Lanka in 2012 and 2013.

"A change of government should not mean a weaker position from Australia on human rights," Labor's foreign affairs spokesman Tanya Plibersek said.

The wording of the mooted new resolution has not been completed but the US has said it would sponsor one. Australia aims to join the human rights council in 2018.